1. Field of The Invention
The present invention relates to an exposure apparatus and a device manufacturing method. More particularly, the present invention relates to an exposure apparatus used in a lithography process in manufacturing semiconductor devices, liquid crystal devices and the like, and a device manufacturing method with which exposure is performed by using the exposure apparatus.
2. Description of The Related Art
Since before, in a lithography process to manufacture semiconductor devices, liquid crystal display devices and the like, a reduction projection exposure apparatus of a step-and-repeat method (a so-called stepper) and a scanning projection exposure apparatus of a step-and-scan method (a so-called scanning stepper) have been mainly used.
In recent years, the exposure apparatuses have used shorter wavelengths for exposure under the demand for improvement of resolution responding to finer circuit patterns in accordance with higher integration of semiconductor devices and the like. Currently, a KrF excimer laser with an oscillation wavelength of 248 nm and an ArF excimer laser with a shorter oscillation wavelength of 193 nm are used as a light source. In the exposure apparatus using such a light source with a short wavelength, from a viewpoint that the sensitivity of resist needs to be increased to compensate for the shortage of brightness of each light source, a high sensitive, chemically amplified resist has been used as the resist that coats a substrate. The sensitive emulsion of the chemically amplified resist contains acid generating agent; catalytic reaction is induced in a subsequent thermal processing (PEB: post-exposure-bake) by the acid generated in exposure, and insolubleness (negative type) or solubleness (positive type) of the resist to a developer is promoted.
It has been found out recently that a trace of gas in the atmosphere causes adverse effect to the exposure apparatus. For example, when a substrate is coated with a positive type chemically amplified resist, a phenomenon occurs that a trace of base gas of a ppb level in the atmosphere neutralizes an acid catalysis generated on the surface of the positive type chemically amplified resist to form a surface hard-soluble layer, and that a resist""s section, which is to be rectangular, is shaped like a visor called a T-shape that resembles a letter T after the exposure and development are performed. Overcoat is needed since the chemically amplified resist as a high sensitive resist cannot be used alone, and thus the throughput reduces.
Moreover, with shorter wavelengths and higher illumination of an exposure beam, for example, ammonia gas, sulfur oxide, organosilicon and the like in the atmosphere chemically react to strong energy of short wavelength ultraviolet light and precipitate on the surfaces of optical elements in the exposure apparatus as tarnish substances. It has been found out that a certain amount of the precipitation causes the scattering and the absorption of light beams and thus phenomena such as the decreases of degree and uniformity of illumination on the irradiated surface. Accordingly, it is becoming a matter of importance to control chemical pollutants in the atmosphere to a low concentration.
For this reason, it is required that the environment inside a current exposure apparatus is strictly controlled.
On the other hand, since the exposure apparatus is an extremely precise apparatus, the temperature state inside the apparatus needs to be controlled to a constant level in order to make each section thereof exert its desired performance. For such temperature control, a conventional exposure apparatus is designed to keep the space inside an environmental chamber in a uniform temperature distribution by sending a gas, whose temperature is controlled by a temperature control unit, into the environmental chamber where the exposure apparatus main body is housed. In addition, to keep the concentration of the foregoing chemical pollutants such as ammonia to a low level, the chemical pollutants need to be removed before the gas whose temperature is controlled is sent into the environmental chamber. For this purpose, a filter unit that removes chemical pollutants in the gas by chemical adsorption and physical adsorption (hereinafter, also referred to as a xe2x80x9cchemical filterxe2x80x9d for convenience) is generally used.
There is no doubt that realization of higher integration of semiconductor devices will be required in future. Accordingly, an exposure apparatus is required to realize even more accurate exposure. Thus, further improvement of performance of each element in the exposure apparatus is demanded. One such demand is further improvement of the temperature control performance inside the environmental chamber.
However, it has been found recently that when gas for air conditioning, e.g., air of which the temperature fluctuation amount relative to a target temperature is strictly controlled to a value or less by an air conditioner or the like is sent into the environmental chamber to highly accurately control the temperature inside the environmental chamber, the temperature fluctuation amount, relative to the target temperature, of the air sent into the chamber increases in the environmental chamber. Therefore, the temperature fluctuation is likely to block the realization of higher exposure accuracy required in the future.
The inventors presumed that constituents for improving the exposure accuracy cause the above increase of the temperature fluctuation amount because it has appeared after the exposure accuracy has become greatly high, and repeated various kinds of experiments and the like under the presumption. As a result, the inventors found out that the temperature fluctuation amount of the air increases after the air passes through the foregoing chemical filter unit rather than before.
The present invention was made based on the foregoing novel findings obtained by the inventors. A first object of the present invention is to provide an exposure apparatus capable of simultaneously limiting the illumination reduction caused by tarnish of optical members and an increase of the temperature fluctuation amount.
A second object of the present invention is to provide a device manufacturing method capable of manufacturing highly integrated micro-devices with good productivity.
According to the first aspect of this invention, there is provided an exposure apparatus, comprising: an exposure apparatus main body that exposes a substrate to an energy beam so as to form a predetermined pattern on said substrate; a main body chamber that encloses at least a portion of said exposure apparatus main body; an environmental control unit connected to said main chamber to supply a predetermined gas into said main body chamber to control an environment inside said main body chamber; and at least one first filter unit that is arranged in a portion of a ventilation path of said gas supplied into said main body chamber by said environmental control unit, removes chemical pollutants from said gas, and controls temperature fluctuation of said gas after passing through the first filter unit to within a predetermined range.
The ventilation path of the gas supplied into the main body chamber by the environmental control unit is not limited to the ventilation path between the environmental control unit and the main body chamber, but specifically includes an air-supply path in the environmental control unit and the main body chamber, in its concept.
With this ventilation path, the first filter unit that removes chemical pollutants from the gas and controls the temperature fluctuation of the gas after passing the filter unit to within the predetermined range is arranged in a portion of the ventilation path of the gas supplied into the main body chamber by the environmental control unit. Accordingly, the space including the ventilation path in the downstream of the first filter unit has an atmosphere from which chemical pollutants is removed and the temperature fluctuation of the gas, whose target temperature has been set by the environmental control unit, after passing the first filter unit is controlled. That is, the atmosphere around the exposure apparatus main body can be kept chemically, highly clean, and occurrence of problems such as the illumination reduction caused by tarnish of the optical members can be effectively controlled for a long period of time. Moreover, the increase of the temperature fluctuation amount of the gas supplied into the main body chamber can be effectively controlled as well.
In this case, said first filter unit may control temperature fluctuation of said gas after passing through the first filter unit such that temperature error, relative to a target temperature, of said gas after passing through lies within a predetermined range. In such a case, the inventors confirmed through experiments that the temperature of the gas after passing the first filter unit can be controlled to a degree of a temperature fluctuation amount with which the performance of the exposure apparatus is maintained for a long period of time.
In addition, as described, the inventors were convinced that the chemical filter unit is a factor to increase the temperature fluctuation amount of the gas after passing the filter unit. The inventors further studied the factors of the temperature fluctuation of the gas after passing the filter unit, and discovered that the humidity fluctuation before passing the filter unit has an influence larger than expected on the temperature of the gas after passing the filter unit.
The followings are considered to be the reason why the humidity fluctuation of the gas before passing the filter unit influences the temperature of the gas after passing the filter unit. When the gas passes the filter unit, exchange of moisture between the filter unit and the gas is performed until equilibrium is reached between the filter unit and the gas. At this point, when the moisture moves (adsorbs) from the gas to the filter unit, heat of adsorption is generated in the filter unit, and the temperature of the gas passing the filter unitrises. When the moisture moves (vaporizes) from the filter unit to the gas, the filter unit is deprived of heat of vaporization, and the temperature of the gas passing the filter unit drops. Accordingly, even if the temperature of the gas passing the filter unit is kept within the predetermined temperature range, the temperature of the gas after passing the filter unit fluctuates because the quantity of heat given or deprived of also fluctuates when the humidity of the gas before passing the filter unit fluctuates.
It is noted that humidity fluctuation before passing through the filter unit corresponds to humidity fluctuation of air in the clean room where the main body chamber is installed. Here, so as to minimize the humidity fluctuation before passing through the filter unit, a function for minimizing the humidity fluctuation may be added to the environmental control unit. Meanwhile, the control of humidity fluctuation, before passing through the filter unit, that is required to adjust the temperature of the gas to a target temperature after passing through the filter unit is smaller than the humidity fluctuation of air in the clean room. If the environmental control unit needs to keep the humidity fluctuation of air in the clean room below the limit, the environmental control unit becomes more expensive in equipment cost and larger.
In an exposure apparatus of the present invention, said first filter unit may comprise a filter section having one or more filter media that remove chemical pollutants contained in said gas and that perform adsorption of moisture in said gas and discharge of moisture into said gas. In such a case, if the adsorption of the moisture in the gas and the discharge of the moisture into the gas by the filter section are controlled to within the predetermined range, the fluctuation of the temperature error of the gas relative to the target temperature before/after passing the filter section can be minimized.
In this case, said filter section may have at least two filter media that are arranged a predetermined distance apart in a passage direction of said gas. In such a case, the adsorption and the discharge of the moisture in the gas can be controlled within the predetermined range without reducing the capability of removing chemical pollutants, and the temperature fluctuation of the gas can be controlled. The reason is considered to be as follows.
Since at least two filter media are arranged along the passage direction of the gas in the predetermined distance, an area where the filter medium does not exist (a mid-space layer) is made in a gap between the filter media. And, the passing of the gas through the first (or a few media in the upstream) filter medium in the gas passage direction allows the gas to give or receive the moisture to or from the filter medium so as to reduce the humidity of the gas when the humidity of the gas is high and so as to increase the humidity of the gas when the humidity of the gas is low, for the same reason as the foregoing. That is, the humidity fluctuation of the gas converges on a constant value. Meanwhile, when the gas passes the subsequent filter media, a moisture quantity of the gas changes little because the humidity is substantially kept at a constant level. Thus, only chemical pollutants are removed from the gas, and the temperature of the gas changes little. In other words, since the temperature change of the gas occurs only in the first (or a few media in the upstream) filter medium in the gas passage direction without reducing the capability of removing chemical pollutants, the adsorption and discharge of the moisture in the gas can be controlled to within the predetermined range and the temperature fluctuation of the gas can be controlled.
In an exposure apparatus of the present invention, at least one of said filter media may have at least one portion of which a packing ratio is set to be lower than the other portions. In such a case, since the adsorption and discharge of the moisture in the gas can be controlled, the temperature error of the gas after passing the first filter unit relative to the target temperature can be minimized.
It is noted that the phrase xe2x80x9cat least one of said filter media may have at least one portion of which a packing ratio is set to be lower than the other portionsxe2x80x9d means not only the case where the packing ratio of a portion of the same filter medium is set to be lower than the other portions, but also the case where a plurality of filter media are used and where the packing ratio is different among the filter media.
In an exposure apparatus of the present invention, said environmental control unit may comprise a gas supply fan that supplies said gas into said main body chamber via said first filter unit and a temperature adjustment unit that adjusts the temperature of said gas to within a predetermined range. In such a case, the gas whose temperature is adjusted within the predetermined range by the temperature adjustment unit is supplied into the main body chamber by the gas supply fan. At this point, the gas supplied from the gas supply fan is supplied into the space via the first filter unit, the temperature change of the gas being small after it passes the first filter unit. Accordingly, a chemically clean gas from which chemical pollutants are sufficiently removed and of which the temperature error relative to the target temperature is sufficiently limited is supplied into the main body chamber (in more detail, downstream of the first filter unit), and thus the chemical environmental condition and temperature condition in the main body chamber can be controlled to desired conditions.
In this case, said temperature adjustment unit may include a cooling unit that cools down said gas supplied by said gas supply fan. In such a case, the temperature of the gas before passing the first filter unit can be adjusted to within a predetermined range by cooling down the gas by the cooling unit when, for example, the gas heated to hotter than the target temperature is supplied from outside.
In this case, said cooling unit may be set to be at such a temperature as does not cause dew condensation on surfaces thereof.
In an exposure apparatus of the present invention, when the temperature adjustment unit comprises a cooling unit, said temperature adjustment unit may further include a heating unit that heats said gas supplied into said main body chamber by said gas supply fan. In such a case, the temperature of the gas before passing the first filter unit can be adjusted to within a predetermined range regardless of the temperature of the gas supplied from outside.
In an exposure apparatus of the present invention, regardless of presence of a cooling unit, said temperature adjustment unit may include a heating unit that heats said gas supplied into said main body chamber by said gas supply fan. In such a case, the temperature of the gas before passing the first filter unit can be adjusted to within a predetermined range by heating the gas when, for example, the gas cooled down to cooler than the target temperature is supplied from outside.
In an exposure apparatus of the present invention, an exposure room that houses said exposure apparatus main body maybe provided in said main body chamber, and said first filter unit may be arranged in a supply path of said gas supplied to said exposure room. In such a case, the first filter unit, which removes chemical pollutants and controls the temperature fluctuation of the gas after passing the filter unit to within a predetermined range, is arranged in the supply path of the gas supplied to the exposure chamber. Accordingly, the chemically clean gas from which chemical pollutants are sufficiently removed and of which the temperature fluctuation is controlled is supplied into the exposure room. Thus, the peripheral atmosphere of the exposure apparatus main body can be kept chemically clean. Further, since the temperature fluctuation of the gas after passing the first filter unit is small, the temperature fluctuation of the gas after passing the filter unit can be controlled within a predetermined range if, for example, the temperature control of the gas is accurately performed by the environmental control unit before the gas passes the first filter unit.
In an exposure apparatus of the present invention, said exposure apparatus main body may include a substrate stage that holds said substrate and an interferometer that measures the position of said substrate stage, and said first filter unit may be arranged in a supply path of said gas supplied into a portion of the space of said main body chamber where said substrate stage and said interferometer are arranged. In such a case, the first filter unit capable of removing chemical pollutants and controlling the temperature fluctuation is arranged in the supply path of the gas supplied into the partial space of the main body chamber where the substrate stage and the interferometer are arranged. Accordingly, the measurement error of the interferometer caused by air variation (temperature variation) can be controlled as much as possible, and positional control of the substrate stage, which particularly requires accuracy, can be performed with the required accuracy.
In an exposure apparatus of the present invention, a substrate transportation system housing chamber, in which a substrate transportation system that carries said substrate into said exposure apparatus main body and that carries said substrate out of said exposure apparatus main body is housed, may be provided in said main body chamber, and said first filter unit may be arranged in a supply path of said gas supplied into said substrate transportation system housing chamber. In such a case, the inside of the substrate transportation system housing chamber in which the substrate transportation system that carries the substrate into the exposure apparatus main body and that carries the substrate out of the exposure apparatus main body is housed can be chemically clean and be stable in temperature. Further, in the case where the chemically amplified resist, which is easily affected by chemical pollutants, coats the substrate, the surface of the chemically amplified resist can be prevented from becoming hard-soluble, in the substrate transportation system housing chamber as well.
In an exposure apparatus of the present invention, a mask transportation system housing chamber, in which a mask transportation system that carries a mask having said pattern formed into said exposure apparatus main body and that carries said mask out of said exposure apparatus main body is housed, may be provided in said main body chamber, and said first filter unit may be arranged in a supply path of said gas supplied into said mask transportation system housing chamber. In such a case, the inside of the mask transportation system housing chamber in which the mask transportation system that carries the mask into the exposure apparatus main body and that carries the mask out of the exposure apparatus main body is housed can be chemically clean and be stable in temperature.
An exposure apparatus according to the present invention may further comprise: a machine chamber that houses at least a portion of said environmental control unit and is connected to said main body chamber to constitute a circulation path of said gas together with said main body chamber; and at least one second filter unit arranged in an exhaust path returning from said main body chamber to said machine chamber, the second filter unit having a higher removal ratio of said chemical pollutants than said first filter unit. In such a case, since the second filter unit is arranged in the exhaust path returning from the main body chamber to the machine chamber, after chemical pollutants coming out of the elements into the gas in the exposure apparatus main body are effectively removed by the second filter unit, the gas is supplied again through the first filter unit into the main body chamber by the environmental control unit, at least a portion of which is housed in the machine chamber. Thus, the peripheral atmosphere of the exposure apparatus main body in the main body chamber can be kept chemically clean, and the illumination reduction and the like caused by tarnish of the optical members can be effectively limited for a long period of time. In addition, the second filter unit removes chemical pollutants, and the chemically clean gas is supplied to the first filter unit. Furthermore, because the temperature fluctuation need not be considered of the exhaust path returning from the main body chamber to the machine chamber, even if the temperature fluctuation of the gas after passing the filter unit is large, the chemically clean gas from which chemical pollutants have been effectively removed can be supplied to the first filter unit by using the filter unit having a high capability of removing chemical pollutants, without causing a problem. Therefore, the lifetime of the first filter unit lengthens, and replacement of the filter is unnecessary for a long period of time.
An exposure apparatus of the present invention may further comprise: a machine chamber that houses at least a portion of said environmental control unit and is provided with an outside gas intake; and at least one second filter unit arranged in a path of outside gas taken in through said outside gas intake, the second filter unit having a higher removal ratio of said chemical pollutants than said first filter unit. In such a case, since the second filter unit is arranged in the path of the gas taken in from the outside air intake provided in the machine chamber, the chemically clean, outside air from which chemical pollutants have been removed by the second filter unit is taken in the unit by the second filter unit. Thus, the peripheral atmosphere of the exposure apparatus main body in the main body chamber can be kept chemically clean, and the illumination reduction and the like caused by tarnish of the optical members can be effectively limited for a long period of time. In addition, the second filter unit removes chemical pollutants, and the chemically clean gas is supplied to the first filter unit. Furthermore, because the temperature fluctuation need not be considered of the path of outside air inside the machine chamber, even if the temperature fluctuation of the gas after passing the filter unit is large, the chemically clean gas from which chemical pollutants have been effectively removed can be supplied to the first filter unit by using the filter unit having a high capability of removing chemical pollutants, without causing a problem. Therefore, the lifetime of the first filter unit lengthens, and replacement of the filter is unnecessary for a long period of time.
In the exposure apparatus of the present invention, the surface of said substrate may be coated with chemically amplified resist as a photosensitive emulsion. In such a case, the surface of the chemically amplified resist can be almost prevented from becoming hard soluble because the inside of the main body chamber can be kept chemically clean.
Furthermore, in the lithography process, the illumination reduction and the like caused by tarnish of the optical members can be effectively limited for a long period of time by performing exposure using an exposure apparatus of the present invention. Thus, highly integrated devices can be manufactured with high productivity while maintaining the high throughput. Therefore, according to the second aspect of this invention, there is provided a device manufacturing method using the exposure apparatus of this invention.